The invention concerns a fuel injector for a fuel injection system, in particular a common rail injection system, for injecting fuel into the combustion chamber of an internal combustion engine. The invention furthermore concerns a method for manufacture and/or assembly of a nozzle needle assembly which can be used in particular in such a fuel injector.
A generic fuel injector is disclosed for example in publication DE 10 2008 002 417 A1. The fuel injector described therein comprises a piezoelectric actuator which is accommodated in a relatively pressureless actuator chamber. The piezoelectric actuator is hydraulically coupled to the nozzle needle of the injector such that the nozzle needle assumes its closed position when the piezoelectric actuator is electrically discharged, and transfers to the opening position when the piezoelectric actuator is connected to an electric power source. This means that the opening stroke of the nozzle needle takes place in the opposite direction to the actuator stroke. The coupling device thus achieves a reversal of the movement direction. This has the advantage that the piezoelectric actuator need only be electrically charged during the brief injection phases and is electrically discharged in the longer rest phases of the fuel injector and hence subject to less strain. As a result the life of the piezoelectric actuator provided for activating the nozzle needle is extended. A further measure extending the life of the piezoelectric actuator is the arrangement of the piezoelectric actuator in a relatively pressureless actuator chamber. The actuator is thus not exposed to fuel under high pressure. No high-pressure-resistant seal of the piezoelectric actuator is therefore required.
The device described in the publication for hydraulic coupling of the piezoelectric actuator with the nozzle needle furthermore allows a distance translation between the stroke of the actuator and the stroke of the nozzle needle, in that the cross sections of the two pistons causing the displacement in the coupling device are dimensioned significantly differently. As a result an adequate nozzle needle stroke can be achieved even with a short actuator stroke.
The invention is based on the object of refining a fuel injector of the type described initially in that a greater clearance exists in relation to the surface area design of the coupler pistons to optimize the distance translation. At the same time the structure of the coupling device and the connection of the coupling device to the nozzle needle are simplified to create a simple fuel injector which can be produced at low cost.